The present invention relates to an intaglio printing machine.
A conventional intaglio printing machine comprises a plate cylinder having a copperplate thereon, a pattern roller which is in rolling contact with the outer surface of the copperplate, and an inking unit with a duct roller in rolling contact with the pattern roller. Ink attached by the inking unit to projections of the pattern roller is filled in recesses as an image portion of the copperplate. The ink attached to a nonimage portion is removed, and the ink left in the recesses is transferred to a sheet fed between the plate cylinder and an impression cylinder under a high pressure, thereby performing intaglio printing.
FIG. 1 is a side sectional view of a conventional intaglio printing machine to explain an ink supply principle. FIG. 2 is a plan view of a banknote 1 as an example of printed matter. The ink supply principle will be described in detail with reference to FIGS. 1 and 2. Assume that a three-color image of the banknote 1 has a dark green pattern 1A representing a peripheral pattern, a sepia pattern 1B representing the right profile and central number, and a dark blue pattern 1C representing the lower left mark, which are formed by three separate printing surfaces. A plate cylinder 2 has a diameter which is three times that of a regular plate cylinder, so that three plates 3 are mounted thereon. Each plate 3 has 18 recesses 3a which constitute a matrix of 6 rows.times.3 columns. The recesses 3a represent the pattern of the banknote 1. The recesses comprise shallow and deep recesses in accordance with the pattern of the banknote. In particular, when a banknote is printed, depths of the recesses 3a fall within the range between 40.mu. and 180.mu.. Three sets of an inking unit 4 and a pattern roller 5 are prepared in accordance with the pattern colors. Only the structure for one pattern color in the intaglio printing machine in FIG. 1 is illustrated. The pattern roller 5 has a diameter about 1/3 that of the plate cylinder 2. The pattern roller 5 has six projections 5a each corresponding to one row of the banknote 1. These projections 5 a are larger than the recesses 3a of the plate 3. For example, when the sepia pattern is to be printed, the recesses 3a constitute the pattern 1B (FIG. 2) representing the profile. The projections 5a cover the area surrounded by the alternate long and short dashed line of FIG. 2. The nonimage portion excluding the projections 5a is engraved to be flat and is not brought into contact with the surface of the plate 3 and a duct roller 6.
With this arrangement, ink 8 stored in an ink duct 7 in the inking unit 4 flows out from a space between the outer surface of the duct roller 6 and the distal end of an ink blade 9 upon rotation of the duct roller 6. The ink 8 (i.e., an ink film 8A) is then applied to the outer surface of the duct roller 6. Upon rotation of the respective duct rollers 6 (the duct roller 6 for the sepia ink in this case), the ink film 8A is transferred as an ink film 8B to the projections 5a of the pattern roller 5 and is filled in the recesses 3a of the plate 3. Since the size of the projections 5a is larger than that of the recesses 3a, the ink film 8B is transferred to part of the nonimage portion around the recesses 3a. However, the excess ink is wiped by a wiping roller 10 rotating in the same direction as that of the plate cylinder 2 before the recesses 3a oppose an impression cylinder. Therefore, only the ink filled in the recess 3a is transferred to the sheet. Reference numeral 11 denotes a vibrating roller for spreading the ink film 8A axially of the duct roller into a uniform thickness. Inks for colors excluding sepia can be supplied in the same manner as described above.
A plurality of adjusting screws 12 are aligned in line along the longitudinal direction of the ink duct 7 in the same manner as in a lithographic press. By moving the adjusting screws 12 back and forth, the ink blade 9 is elastically deformed to adjust ink outflow spaces between the duct roller 6 and the ink blade 9 in units of sections along the direction of width of the ink blade. As a result, the amount of ink required for the respective recesses 3a in the plate 3, that is, the amount of ink properly filled in the respective recesses 3a can be adjusted.
In conventional ink quantity adjustment by the adjusting screws 12, the ink blade 9 cannot precisely respond upon back-and-forth movement of the adjusting screws 12, thus resulting in coarse adjustment. In this case, an amount of ink smaller than a total amount of ink to be filled in the recesses 3a is supplied, thereby causing some of the recesses 3a to be insufficiently supplied with ink and resulting in a frequent occurrence of a printing error called blinding. In order to prevent blinding, excess ink is supplied to the recesses 3a in accordance with the proper amount of ink required for the deepest recesses. The excess ink is removed by the wiping roller 10. The removed ink cannot be reused and is disposed of, thus wasting the ink. Together with this disadvantage, the performance of the wiping unit is degraded and its service life is shortened. In the state-of-the-art printing techniques, the adjusting screws can be adjusted along only the direction of width of the ink film 8a. Under these circumstances, the projections 5a of the pattern roller 5 must be increased in size by a sufficient margin, thereby further increasing ink consumption.